1. I am using Google Keyboard. I am using Nexus 6P and bunch of other phablet. Never had issue with gesture typing using one hand.
2. Not really gonna aruge with rest of stuff. Nexus 6P battery life isn't the best. Remember, it uses higher end SOC and QHD display. My Nexus 6P easily last me for a day with lots of WeChat, WhatsApp, Youtube usage during the day (1 hours lunch time streamming Youtube and half hour break time). Battery still around 15%.
3. Regarding to live photo and 3D Touch, i rarely use it with my iPhone 6S. 3D touch is all guessing game, some app support some app does not. And really, 3D Touch does not save time anyway. Live Photo is just gemmick. I don't see the value behind it.
4. Regarding to 720P or higher. When you watch high definition video or high resolution picture, sub 720P just does not show all the details. QHD screen provide much more details than sub 720P SE screen. Take a look at MKBHD's video regarding to QHD screen.
5. I do agree that iOS provide great user experiences in terms of general performance. Though, Android now days runs just as good if not better. I am typing this with $150 Meizu M2 Note, it runs really fast. In terms of battery life, iPhone certainly provides good battery life, it is certainly not the best. Espepecially, when i can top up 7 hours of use with 10 minutes of charge with Nexus 6P.
6. One thing i wanted to point out is that iOS proivdes almost no one hand use optimization. Wherr on Android there are few ways to use large phone one hand. For example, Meizu's flyme UI allows me to swip from bottom to invoke mutlitasking card view, the smart touch function allows me to swipe down from any where get notifcation sheet. The flooding circle allows me swip up get back to home screen, swipe left and right to swich between apps. Tap once go back tap twich go forward. Lots of Android phones allows you to shrink entire UI to 4 inch size, so you can use it one hand. The UI itself stay at that size, does not go back until you set it back to full screen. The only thing iPhone SE provide is small size. It is maybe easier to pocket, but not so much. With lots of 5 inch Android phone sized similar with iPhone 6S, those phablet can easily be pocketed. One hand usage can be done by software optimization.
My take is phablet provide much better experiences than small form factors. Short comings can be fixed by using software optimization. I personally would not go back, i even think my iPhone 6S is too small.
I wouldn't consider Qualcomm's snapdragon series SoC as 'higher end' than Apple's internally designed SoC's. In most benchmarks it outperforms Qualcomm's competition. QHD is 960x540, the iPhone SE pushes pixels at 1136x640. I'm not sure where you're going with this. In the end PPI is more important than effective resolution, as the size of the display is the differentiator. A 720p feed on a 120 inch display for instance, will look like complete crap.